In existing aircraft, the turbofan engines such as turbojet engines are suspended beneath the wing by complex attachment devices, also known as
“EMS” (for “Engine Mounting Structure”), or attachment pylons. The attachment devices conventionally used have a primary structure, also known as rigid structure, that is frequently produced in the form of a single box, that is to say is made up of the assembly of lower and upper spars that are connected together by a plurality of transverse ribs situated inside the box. The spars are arranged on lower and upper faces, while lateral panels close the lateral faces of the box. In addition, the attachment pylon is arranged in the upper part of the engine, between the latter and the wing box. This position is known as the “12 o'clock” position.
As is known, the primary structure of these pylons is designed to allow the static and dynamic loads generated by the engines, such as the weight, the thrust, or even the various dynamic loads, in particular those associated with cases of failure such as: loss of blades (FBO), collapse of the front landing gear, hard landing, etc. to be transmitted to the wing.
In attachment pylons known from the prior art, the transmission of loads between its primary structure, known in the form of a single box, and the wing is conventionally ensured by a set of mounts comprising a front mount, a rear mount, and an intermediate mount intended in particular to react thrust loads generated by the engine.
In recent turbofan engines, the high bypass ratio that is desired has resulted in extremely high bulk, since an increase in the bypass ratio inevitably causes an increase in the diameter of the engine, and more particularly an increase in the diameter of its fan casing.
Thus, with a ground clearance which is fixed so as to remain acceptable from a safety point of view, the space remaining between the wing element and the engine becomes increasingly small, or even non-existent for engines with a high bypass ratio. As a result, it can prove difficult to install the attachment pylon and the various wing mounts in this remaining vertical space that is usually devoted to this installation.
The evolution of turbofan engines has therefore had the detrimental effect of imposing a reduction in the vertical dimensions of the attachment pylon, in particular so as to be able to preserve enough space to fit the mount fittings. The large dimensions of some mounts are necessitated by the need to react the engine thrust loads, that is to say those oriented in the longitudinal direction of this engine, and those oriented in the transverse direction thereof. By way of indication, it is recalled that the longitudinal direction of the engine corresponds to the direction of the main axis of rotation of the propulsion system.
However, the options for reducing the vertical dimensions of the attachment pylon are limited. Specifically, the rigid structure of this pylon, also known as primary structure, needs to have sufficient dimensions to afford mechanical strength capable of withstanding the transmission of loads from the engine to the wing element, with small deformation under stress in order not to impair the aerodynamic performance of the propulsion system.
In the prior art, multiple solutions have been proposed for bringing the engine as close as possible to the wing element from which it is suspended, this being in order to maintain the required ground clearance, in particular with regard to the risks of ingestion and collision, also known as the FOD (Foreign Object Damage) risk. Nevertheless, these solutions need to be constantly improved upon in order to adapt to the increasingly high diameters of fan casing adopted in order to meet bypass ratio requirements.